The most typical use of the Provisioning service is to periodically back up ENC databases to the ENS. The back up process works correctly but regardless of how the retention policy properties in the NiagaraNetworkJobPrototype are defined it will not remove the older back up files.
I/A Series (Niagara) all G3 releases
This is a known issue. Software development is investigating the issue.
Until the NiagaraNetworkJobPrototype retention policy functionality is repaired manual maintenance of back up files is required.